DESCRIPTION: Oligodendrocytes play a crucial role within the central nervous system (CNS) through the elaboration of the myelin sheath. Alterations in their function can disrupt myelinogenesis and lead to severe neurological deficits such as those seen in multiple sclerosis and other demyelinating diseases. In oligodendrocytes, as in all cells, normal cellular physiology is dependent upon genomic stability Yet, cellular genomes are constantly exposed to external agents such as environmental chemicals that modify DNA. Additionally, a significant level of endogenous DNA damage arises from hydrolytic decay involving depurination, DNA methylation through non-enzymatic alkylation of bases by S-adenosylmethinonine, and free radical-induced damage either from reactive oxygen species or from nitric oxide. Investigating the types of lesion formed and their repair are of prime importance in determining the impact that exposure to specific toxins will have on a particular target, such as an oligodendrocyte. An understanding of these interactions is essential to elucidate how environmental toxins are involved in the etiology and pathogenesis of demyelinating diseases. Therefore, this competitive renewal will remain focused on the mechanisms by which cells of the CNS, particularly oligodendrocytes, deal with insults to their DNA. The objective of this proposal is to explore the factors which regulate damage and repair of specific lesions in DNA. Three specific aims are proposed. The first is to investigate repair of alkylation damage. These studies will use a monoclonal antibody against O6-methylguanine combined with quantitative PCR to determine repair of this mutagenic DNA adduct in specific transcribed and nontranscribed nuclear sequences. Repair of N-methylpurines, at the level of individual nucleotides, will be investigated using LMPCR. The second aim is to evaluate the formation and repair of reactive oxygen radical-induced DNA damage. These studies will assess repair across the entire genome, within specific DNA sequences, and at the level of individual nucleotides. The third aim will examine formation and repair of specific types of DNA damage induced by nitric oxide. When successfully completed, these studies will enhance our understanding of the role that environmental toxins play in the etiology and pathogenesis of demyelinating diseases. Moreover, knowledge of the molecular mechanism whereby xenobiotics interact with the DNA of oligodendrocytes will facilitate the development of preventative and therapeutic strategies for demyelinating diseases.